Link a Texture to Displace Modifier using Python
I had a similar issue and solved it this way. I was trying to create a blobbiness effect:

Make base object:

import bpy
bpy.ops.mesh.primitive_ico_sphere_add(subdivisions = 6, size = 1.0, location = [0.,0.,0.])
base_geometry = bpy.data.objects['Icosphere']
base_geometry.name = 'Base_Geometry'


I add this by default, you can't apply modifiers in edit mode, this assumes the object is already selected:

bpy.ops.object.mode_set(mode='OBJECT')


Make texture:

tex = bpy.data.textures.new("Voronoi", 'VORONOI')
tex.distance_metric = 'DISTANCE_SQUARED'


Make the modifier, set settings, and apply:

modifier = base_geometry.modifiers.new(name="Displace", type='DISPLACE')
modifier.texture = bpy.data.textures['Voronoi']
modifier.strength = -0.2
bpy.ops.object.modifier_apply(apply_as='DATA',modifier='Displace')


Hope it helps